In recent years, from the viewpoint of the effective utilization of resources, the prevention of environmental pollution, or the like, solar batteries that directly convert sunlight into electric energy have received attention, and the development of the solar batteries has been pursued.
A solar battery generally has a configuration in which cells 4 for a solar battery, such as silicon power devices, are sealed with sealing films 3A and 3B, which are EVA (ethylene-vinyl acetate copolymer) films, between a glass substrate as a front side transparent protective member 1 and a back side protective member (back cover) 2, as illustrated in FIG. 1. Hereinafter, a sealing film that is disposed in the light receiving surface side of the cells is referred to as “front side sealing film” and a sealing film that is disposed in the back side of the cells is referred to as “back side sealing film.”
The front side transparent protective member 1, the front side sealing film 3A, the cells 4 for a solar battery, the back side sealing film 3B, and the back side protective member 2 are layered in this order, heated and pressurized, and adhesively integrated by crosslinking and curing the EVA, to manufacture such a solar battery.
In accordance with the above-described solar battery, it is strongly desired to enable light incident on the solar battery to be taken into the cells for a solar battery as efficiently as possible from the viewpoint of improving power generation efficiency. Thus, the EVA films for sealing, which have maximum transparency and do not absorb or reflect incident sunlight and through which the sunlight almost passes, are desirable.
However, the occurrence of the phenomenon of yellowing EVA films for sealing to decrease a sunlight transmittance due to the influence of light and heat, when a solar battery is used for a long term, and poor appearance caused by the yellowing have become problems.
For these problems, there have been disclosed the measures of using various additives such as various organic peroxides and ultraviolet absorbers together in EVA films for sealing, and the like. For example, in Patent Document 1, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, which is a peroxyester-based peroxide, is used as an organic peroxide (crosslinking agent), and 2-hydroxy-4-n-octoxybenzophenone, based on monohydroxyalkoxybenzophenone, is used as an ultraviolet absorber. In addition, in Patent Document 2, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane is used as an organic peroxide, and 2-hydroxy-4-n-octoxybenzophenone, which is the same as described above, is used as an ultraviolet absorber.